/*
 * Funambol is a mobile platform developed by Funambol, Inc. 
 * Copyright (C) 2003 - 2007 Funambol, Inc.
 * 
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License version 3 as published by
 * the Free Software Foundation with the addition of the following permission 
 * added to Section 15 as permitted in Section 7(a): FOR ANY PART OF THE COVERED
 * WORK IN WHICH THE COPYRIGHT IS OWNED BY FUNAMBOL, FUNAMBOL DISCLAIMS THE 
 * WARRANTY OF NON INFRINGEMENT  OF THIRD PARTY RIGHTS.
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Affero General Public License 
 * along with this program; if not, see http://www.gnu.org/licenses or write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02110-1301 USA.
 * 
 * You can contact Funambol, Inc. headquarters at 643 Bair Island Road, Suite 
 * 305, Redwood City, CA 94063, USA, or at email address info@funambol.com.
 * 
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General Public License version 3.
 * 
 * In accordance with Section 7(b) of the GNU Affero General Public License
 * version 3, these Appropriate Legal Notices must retain the display of the
 * "Powered by Funambol" logo. If the display of the logo is not reasonably 
 * feasible for technical reasons, the Appropriate Legal Notices must display
 * the words "Powered by Funambol".
 */

package com.funambol.util;

import java.util.Stack;
import javax.microedition.lcdui.List;

/**
 * A multithreaded queue used for 
 * implementing producer-consumer style threading patterns.
 * Multiple threads can wait for runnable objects being added
 * to the queue while other threads add to the queue.
 */
public class Queue {

    private Stack tasks = new Stack();
    private long defaultTimeout = 100;

    public Queue() {
    }

    /**
     * Returns the current number of runnable objects in the queue
     */
    public synchronized int size() {
        return tasks.size();
    }

    /** 
     * adds a runnable object to the end of the queue.
     * At least one thread will be notified.
     */
    public synchronized void add(Object runnable) {
        tasks.push(runnable);
        notifyAll();
    }

    /** 
     * Removes the first runnable object from the queue, blocking until one is available.
     */
    public synchronized Object remove() {
        while (true) {
            Object runnable = removeNoWait();
            if ( runnable != null ) {
                return runnable;
            }
            try {
                wait( defaultTimeout );
            }
            catch (InterruptedException e) {
                e.printStackTrace();
                Log.error(this, "InterruptedException  in remove() method");
            }
        }
    }

    /**
     * Removes the first runnable object from the queue without blocking.
     * This method will return immediately with an item from the queue or null.
     * @return the first runnable object removed from the queue or null if the
     * queue is empty
     */
    public synchronized Object removeNoWait() {
        if ( ! tasks.empty() ) {
            return tasks.pop();
        } else {
            return null;
        }
    }

}